Schwarzschild Radius Calculator
Find the event-horizon radius of a black hole of a given mass — the size to which any mass must be crushed to become one.
How it works
r_s = 2·G·M ÷ c² · c = 299,792,458 m/s
The Schwarzschild radius is the radius of the event horizon of a non-rotating black hole — the boundary from within which nothing, not even light, can escape. Any mass compressed inside its own Schwarzschild radius becomes a black hole. The radius is directly proportional to mass, so a more massive black hole is physically larger.
Worked example
For one solar mass (1.989×10³⁰ kg): r_s = 2 × 6.674×10⁻¹¹ × 1.989×10³⁰ ÷ (299,792,458)² ≈ 2,954 m ≈ 2.95 km. The Sun would have to be crushed to a 3 km ball to become a black hole.
Sources: Schwarzschild radius — Wikipedia
Frequently asked questions
What would happen if Earth became a black hole?
Earth’s Schwarzschild radius is only about 8.9 mm, so all of Earth would have to be squeezed into a sphere the size of a marble. Its gravity at a distance would be unchanged, but nothing could escape from within 9 mm of the centre.
Is the Schwarzschild radius the black hole’s actual size?
It marks the event horizon, the point of no return, not a solid surface. The mass itself is thought to collapse to a much smaller region (a singularity) inside it.
Does a rotating black hole have this exact radius?
The Schwarzschild solution is for a non-rotating, uncharged black hole. Spinning (Kerr) black holes have a somewhat smaller horizon for the same mass, but this formula gives the standard reference value.
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This calculator is for educational purposes. Double-check important results before acting on them.